Sous vide setup mk 3

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The cooker in situ above a water bath

The sous vide setup mk 1 is fine for getting started, but doesn't have sufficient capacity for most meals. Make magazine has a good description of how to make such a cooker. However, not all of the parts are easily available in the UK, so some modification was needed. In addition, it has some problems which meant it wasn't a long-term solution (see the sous vide setup mk 2 for learning about it the hard way). The problems were:

  1. aquarium motors are only rated up to about 35⁰C, and stop working at sous vide cooking temperatures
  2. perspex softens in heat. so motor mounts and supports will fail at sous vide temperatures
  3. the Fotek SSR requires a heat sink for when its drawing current
  4. the geometry of having the box sticking out into the water bath wastes a lot of space

The general principle was fine, but it needed some modification. The cooker unit contains heating elements, a thermocouple, the temperature controller, and an aquarium pump (to mix the water). The whole lot is in a single box, ready to be placed on the edge of any convenient water bath. The alternative is to have two separate boxes, one containing the controller and relay, the other housing the heaters and thermocouple. Two boxes means having less to mount over the water bath, but at the expense of having many leads between the two (swiched mains for the heaters, 12V for the pump, and the thermocouple lead.)

Although this description is fairly self-contained, you'll need to read the original project description for these variations to make sense.

Parts

The underside of the cooker, showing how the components are arranged
  • Heaters: There are plenty of 110V in-cup immersion heaters available on eBay, but very few 240V ones with a decent power rating. I ended up getting some Russian ones from an eBay seller in Ukraine. The plus side is that they're 500W heaters rather than the 300W ones in the original article. That makes the cooker capable of heating quite large water volumes (30l - 40l). The down side is that they're quite a lot larger than the baseline version, so that makes the whole unit much bigger.
  • Enclosure: Make sure you get one that's big enough to hold the controller and the heaters. I ended up getting a monster box with dimensions 21cm × 13cm × 9cm. It needs to be that big to fit the 16cm required of the three heaters and pump in a line.
  • Controller: I reused the TET 612 from the Sous vide setup mk 1.
  • Temperature sensor: Again, I reused the type J thermocouple from the Sous vide setup mk 1 rather than the PT100 platinum temperature-dependent resistor from Make.
  • Relay: The easiest solid-state relay (SSR) for me to get hold of (Fotek SSR 25-DA) has screw-down terminal blocks, so no need for any soldering. It's also bigger than the one in Make, but I had plenty of room in my monster box. The downside is that it needs a heatsink block, which takes up a lot of the room in the monster box...
  • Circulation pump: a P-38B 12V DC Submersible Water Pump, a submersible pump rated up to 80⁰C that pushes out 7.2l/min (95 gal/hr), allowing the heater to use water baths up to around 35l.
  • A power supply for the pump. I used a replacement LCD monitor power supply. The 5A it can supply is vastly more than the pump needs, but that power supply is
    • easily available, and
    • unlikely to fail due to operating near its limits.
It also takes up a lot of room.

Materials

  • Glue: Hot glue gets used a lot in this project, but not all hot glues are made equal. Most hot glues melt at around 105⁰C which means that, at the temperatures reached while cooking, the glue has softened considerably and everything falls apart. This is both disappointing and the cause of many sarcastic comments from spouses. But all is not lost! You can get high-temperature glue that melts at 165⁰C, which remains stable at sous vide temperatures. High-temperature (and dual-temperature) glue guns are quite common, but the glue is rarer. Make sure you also get glue that only melts at the higher temperature: dual-temperature-compatible glue will still melt at the lower temperature, so won't do.
  • Sealant: This also gets used a lot in this project. Make sure you use bathroom/kitchen sealant (the kind that smells of vinegar as it cures) rather than the cheaper generic sealant. The generic stuff falls apart when held over hot water for several hours.
  • Switch: I didn't bother with an additional power switch in the cooker. I just use the wall socket switch to control it.
  • Aluminium project box: one that's formed from two C-shaped pieces. One half forms the mount for the cooker, the other is sacrificed to make the pump mount.
  • Loop-ended bolts and nuts: two of these to hold the cooker in place.
  • Zinc sheet: for sacrificial anodes. Steel in hot water rusts quickly, so I used zinc washers to protect all the submerged nuts and bolts and the heating elements.

Construction

The arrangement of parts inside the box
  1. Ensure you have sufficient room on the base of your box for all the components. You'll need the three heaters inline, with the pump outflow pushing water along the centre of the heater coils. The thermocouple should go adjacent to the pump, upstream of the heaters. You'll also need room for the clamp.
  2. Space inside the box is tight, too. Make sure you know where all the components are going. I had to saw off the corner of the base of the relay's heat sink to allow the pump power lead into the box. The 12V power supply has to go on the opposite side of the box from the heaters, which limits places where the power cable can come in from outside. Also, you probably won't be able to mount the controller directly above the heaters, due to lack of vertical space.
  3. Drill the holes in the side of the mounting bracket for the mounting bolts. Use two-part epoxy glue to fix the nuts on the inside of the bracket.
  4. Start by laying out the heaters and pump on the base of the box. Place the heaters as close to the edge as you can while still being able to put glue all round them inside the box. You'll also need to leave room for the mounting bracket.
  5. Make the holes for the heaters and insert them without gluing. Then fix the position of the pump and mounting bracket. You want the pump outflow to be directed through the middle of all three heater coils. Ensure that the pump bracket doesn't overlap the line of where the mounting bracket will be, so that the mounting bracket is the only part that touches the side of the tank.
  6. Make the hole for the thermocouple.
  7. Make holes for the power lead and controller. You may need to trim the lip around the lid of the box where the controller is.
  8. Glue the heaters in place, and screw in the pump bracket, pump, and mounting bracket. I added home-made zinc washers to all the bolts, as sacrificial anodes.
  9. Do all the wiring inside before fixing any components. It'll turn into a bit of a rats nest, but that can't be helped.
  10. Attach the SSR to its heat sink.
  11. Use two-part epoxy glue to secure the SSR heat sink and 12V power supply in place.
  12. The controller stays in place by friction, especially when the lid is secured.

Wiring

Wiring for the cooker

The wiring mostly follows from that in Make. A solid-state relay (SSR) controls power to the heaters. The SSR is controlled by the TET-612 controller with input from the thermocouple. The pump is permanently on while power is supplied to the unit.

The connections between the parts are made via screw-down connector blocks. After making all the connections, cover all the terminals with insulation tape to prevent accidental short circuits.

Make sure all wires and connectors can take the load: the heaters will draw 1500W at 240VAC, so the unit as a whole could draw over 7A.

Not shown on the wiring diagram is an earth connection from the mains to the pump. The heaters have no earth connections.

Controller parameters

Press set, enter the passcode 0089, and set up the controller parameters as below.

Parameter Value Comment
Inty J Input type: Type J thermocouple
Outy 2 Use the SSR output for control
Hy 0003 Not used
Psb 0 Not used
Rd 0 Controls a heater, not a cooler
CorF 0 Units: 0 = Celsius

You might as well also set the alarm thresholds. Enter passcode 0001 and set the alarms as

Parameter Value
Sv 62
AH1 100
AL1 95
AH2 85
AL2 90

Controller tuning

The TET 612 is a PID controller and its parameters need to be tuned to control the cooker effectively. The easiest way is for the controller to self-tune by pressing and holding the '>' button until the display flashes.

You will need to set the 'SouF' and 'ot' parameters before doing the tuning.

The controller will move the water temperature above and below the target three times, so it could take up to an hour to do.

To examine or manually adjust the parameters, press set and enter the passcode 0036. Should you be interested, these are the parameters I have.

Parameter Value
P 0.4
I 756
d 189
SouF 0.3
ot 2
Filt 0

In use

  • Don't turn on the cooker unless the heaters are immersed in water above their 'shoulders'. They'll burn out in a very few seconds otherwise. The pump will also burn out quickly if it isn't immersed in water.

Alternative pumps

The hardest part to sources is a pump that is capable of handling water at 80⁰C+ but still small and cheap enough to be viable the cooker. The P38-B is the best I could find. Alternatives are:

All the pumps require an additional power supply.

See also